Cartilaginous (hyaline and fibrocartilage) tissue plays a key role in the articular mechanics of a joint and serves two main functions: first, in association with the synovial liquid, it serves as a dynamic function that decreases the friction force applied to the bones constituting the joint; second, it serves as a static function, which enables the transmission, the dispersion and the damping of the applied constraints. Hyaline cartilage is found lining the bearing surfaces of joints. Hyaline cartilage is avascular, and therefore not prone to regeneration. On the contrary, fibrocartilage (e.g. meniscus) is partially vascular and is able to partially or total self repair. In each case, cartilaginous tissue may be affected with lesions, i.e., abnormalities that affect thickness, surface architecture and internal architectures and biochemical constituents. These lesions may lead to altered joint mechanics with significant functional impairment and disability.
Different diseases are encountered in clinical practice that can affect articular cartilage. For instance, osteoarthritis (OA) is the most common disease. It has been estimated that 63 to 85 percent of Americans over age 65 have radiographic signs of OA (See Yelin E. Impact of musculoskeletal conditions on the elderly. Geriatr Med Today. 1989. (8)3:103-18). Cartilage abnormalities may also occur from post-traumatic or inflammatory etiologies, either of which can predispose the individual to develop secondary OA. Assessment of cartilaginous tissue during the different steps of cartilage disease (diagnosis, treatment, follow-up) is currently based on several imaging modalities. For instance, arthroscopy, which enables direct visualization of cartilage and its injuries (e.g. cartilage defects), magnetic resonance imaging (MRI) with different techniques to assess cartilage tissue, ultrasound imaging (US), optical coherence tomography (OCT) and its derivative (for example PS-OCT), and infra-red (IR) spectrometry analysis all may be identified among the different modalities of cartilaginous tissue assessment. Each has its own advantages and limitations.
Several different types of procedures currently exist for the surgical treatment of osteochondral injuries consisting of full-thickness or partial-thickness chondral defects. These include marrow stimulation, autologous chondrocyte implantation, or osteochondral transplantation. Cartilage procedures are most commonly performed in the knee, but can also be performed in the shoulder, hip, ankle and other joints. While much of the focus in cartilage restorative treatment has been on the repair of full-thickness chondral defects, it is now thought that that earlier treatment of cartilage injuries may delay or prevent irreversible damage. The arthroscopic stabilization of partial-thickness chondral defects obviates the need for more invasive procedures such as partial or total joint arthroplasty.
Traditionally, surgeons have used direct visualization to inspect articular cartilage vis a vis arthroscopy. The advent of advanced imaging techniques provides additional information, but ultimately any intervention has relied on direct visualization. This fundamentally requires changes in cartilage surface morphology on a scale large enough to detect visually. Secondly, the geographic nature of articular abnormalities are often more complex than simple geometric shapes, limiting the efficiency of a simple visual assessment. As surgeons begin to treat these complex articular cartilage lesions earlier in the disease process, identifying and precisely mapping the location and extent of such lesions using minimally invasive techniques becomes increasing difficult. Furthermore, locating and evaluating healthy candidate cartilage sites in autologous implantations or transplantations can be a difficult and subjective task with specimens typically obtained from common anatomical areas (i.e., trochlea of the knee), not specific to the individual patient.
Given the extent of the information and lack of visual cues available to the surgeon, it becomes an overwhelming task to integrate the complex 2-D or 3-D geometry and the extent of cartilage disease and produce a rationale for treatment. Presurgical planning becomes necessary, using all the imaging tools available. However, it is necessary to have a method that integrates all this information for them at the time of surgery without the need to mentally create and store a 3D representation of the cartilage surface. Nevertheless, this 3D integration and representation remains challenging and potentially problematic, with possibility of inaccuracy that might negatively impact surgical outcome.
U.S. Pat. No. 7,184,814 B2 entitled “assessing the condition of a joint and assessing cartilage loss” by Philipp Lang et al. discloses methods for assessing cartilage or disease in a living subject. These assessments are based on a three-dimensional volumetric data-set and representation of joint cartilage, including volume, thickness, biochemical contents, or MRI relaxation time of both normal and damaged or diseased cartilage. Correlation of these biomechanical parameters can be obtained with respect to gait analysis by measuring in vivo limb segment movement from skin placed marker clusters (Point Cluster Techniques). Merged or fused with previous morphological and biochemical data, these biomechanical data can therefore be displayed simultaneously, in order to assess the relationships between the cartilage wear and the joint movement.
The authors also describe methods to perform quantitative cartilage follow-up examinations so that cartilage therapies can be monitored. Although different techniques to obtain an image of the cartilage of the joint are mentioned (ultrasound imaging, computed tomography), the authors predominantly rely on 2D or 3D MRI as the method of choice to obtain representations of the cartilage. Although this technique has certain advantages, it also presents significant limitations: it is expensive (in comparison with ultrasound imaging, for instance) and is subject to motion degradation. The ability to perform real-time MR imaging in conjunction with interventional procedures, such as arthroscopy, is not generally available, and could be prohibitively expensive. Thus, it is not generally possible for a surgeon to perform multiple evaluations of cartilage parameters and update a pre-existing model of the joint during arthroscopy. However, a readily updatable cartilage model would offer many advantages to the surgeon who may want to perform multiple cartilage assessments during an arthroscopic repair. A practical example would be optimal placement of a cartilage graft that is implanted into a defect. Real time evaluation of the morphology of the reconstructed surface would be very useful to minimize any residual contour irregularity.
United States Patent Application Publication No. 2005/0257379 entitled ‘Surgical system for the preparation of an implant and method for the preparation of an implant’ by Giordano et al. discloses a method to quantitatively measure the size, shape, height and/or volume of a cartilage defect. Measurement of the size, shape, height and/or volume of a defect helps the surgeon to select and to prepare an implant so that it better matches and fills the space of the defect. The geometrical parameters of the defect are measured using a position measurement system and a tracked probe having a calibrated tip that is inserted into the joint and positioned in contact with the cartilage surface. The defect can therefore be palpated with the probe tip under arthroscopy, and the boundary line of the defect as outlined by the surgeon can be recorded. Giordano et al. also propose to use an imaging unit connected to the position measuring system to acquire at least one defect image from which boundary information will be extracted. This avoids having to directly contact the cartilage surface. A disadvantage of Giordano's system and method is that the invention provides a tool that the surgeon can use only to outline and size a defect; it provides no assistance to the surgeon to assess the quality of the surrounding cartilage in order to help them determine if it is truly defective or not. It is therefore applicable only to defects in bone/cartilage which are being prepared to be filled by an implant, and it cannot provide any information to aid the assessment of the remaining articular cartilage. In particular, the Giordano system provides no means for quantification of any of the following parameters:                overall or local cartilage surface texture or roughness;        distance between the cartilage surface and the underlying subchondral bone, (i.e. the thickness of the remaining cartilage surface);        bio-material properties of the cartilage such as the cartilage stiffness; and        cartilage subsurface ultra-structural and biochemical properties.Finally, no features are provided to help the surgeon visualize and interpret these data on a realistic and precise model of the joint under examination.        
It would be of value to have improved methods and/or devices that enable the acquisition, interpretation, and utilization of 3D multimodality data on articular cartilage in an integrated, flexible and updatable manner. This capability assists the arthroscopist in the ongoing assessment of any intervention, as well as the providing an updated model to evaluate the need for any further adjustments to the intervention. All of the abovementioned references are hereby incorporated by reference in their entirety.